Electric circuit breaker



Dec. 16, 1958 w, COBURN 2,864,914

ELECTRIC CIRCUIT BREAKER Filed March 15, 1955 5 Sheefts-Sheet l hwuxtorich A. LL/W .%M%M(M 12 Attorneys Dec. 16, 1958 w. A. COBURN 2,864,914

ELECTRIC CIRCUIT BREAKER Filed March 15, 1955 5 Sheets-Sheet 2 AttorneysDec. 16, 1958 w. CQBURN 2,864,914

ELECTRIC CIRCUIT BREAKER Filed March 15, 1955 5 Sheets-Sheet 3 97 99 10079 99 77 I0 57 M 92 76 w B9 as -5 M L @1175 I," a b2 59 O 7 63 m m u u v4,9570 104- 1 8 I9 5 y 16 5 0555 17 k Z W l) 16 14 lhvuxtor ,d'Atter-mays Dec. 16, 1958 w, COBURN 2,864,914

- ELECTRIC CIRCUIT BREAKER Filed March 15, 1955 5 Sheets-Sheet 4 -10 1O'90 50 7o 90 Ambient Tampamburo Fabruxhut Dec. 16, 1958 w. A. COBURN 9.1

ELECTRIC CIRCUIT BREAKER Filed March 15, 1955 I 5 Sheets-Sheet 5 UnitedStates ELECTRIC CIRCUIT BREAKER Wallace A. Coburn, Brandon, Manitoba,Canada, assignor to C. T. Electrical Controls Limited, Brandon,Manitoba, Canada Application March 15, 1955, Serial No. 434,343 Claimspriority, application Canada January 27, 1955 13 Claims. (Cl. 260-116)This invention relates to improvements in electric circuit breakers, andmore particularly to current totalizing circuit breakers of the typedescribed in United States Patent No. 2,600,734, issued to W. A. CoburnJune 17, 1952.

One form of breaker constructed in accordance with Fig. 4 is afragmentary view of the mechanism of the circuit breaker as viewed inFig. 2, but in a different position;

Fig. 5 is a further fragmentary view of the mechanism seen in Fig. 2,many of the parts being shown in section along the line 55 of Fig. 1;

Fig. 6 is a sectional view along the line 6-6 of Fig. 1;

Fig. 7 is a view similar to Fig. 5, but showing the parts in a positionintermediate that of Fig. 5 and Fig. 4; and

Fig. 8 is a diagram illustrating the operational advan tages of thecircuit breaker seen in the other views.

Figures 9 to 11 are a series of diagrams demonstrating the mechanicaloperation of the circuit breaker seen in Figures 1 to 6, by showing asimplified version of certain parts of the same in three differentpositions.

This circuit breaker consists of a body shell 11 moulded from a suitablenon-conducting synthetic resinous material, with a cover 12 moulded froma similar material. The underside of the shell 11 is formed with threeparal lel longitudinally extending cavities 13, 14 and 15 (as best seenin Fig. 6), the central cavity 15 being substantially deeper than theouter cavities 13 and 14. On its upper side the shell 11 has twoparallel longitudinally extending cavities 16 and 17, with a platform 18extending therebetween.

The platform 18 has a transverse passage 19 (see Figs. 2, 3, 4, 5 and7), this passage interconnecting the cavities 16 and 17 andaccommodating a totalizing bar 2%) of insulating material extendingtransversely across the circuit breaker. This bar has bosses 21 (seeFig. 6) projecting downwardly into cavities 16 and 17. These bosses 21are each formed with a rectangular hole 22, through each of which abimetallic strip 23 extends, whereby upward movement of the metallicstrips 23 may be transferred to the bar through adjusting screws 24.

One end of each of the bimetallic strips 23 is fastened to terminals 25by rivets 26 (see Fig. 3). In use, wires (not shown) are connected tothese terminals 25 by screws 27. The free end of each of the bimetallicstrips 23 passes through one of the rectangular holes 22 in the bosses21 of the bar 20, and carries a flexible connecting wire 29 wherebyindividual circuits are completed from 'ice the terminals 25 through thebimetallic strips 23 to a pair of movable contacts 28.

These movable contacts 28 (as best seen in Fig. 2) each consist of abent strip of conducting metal, such as copper, the lower end 30 of eachof these contacts 28 being permanently secured to an insulating carrierbar 33 extending transversely across the circuit breaker. The upper endof each of the contacts 28 carries a raised contact-making surface 34 ofsuitable material such as silver.

The carrier bar 33 which carries the contacts 28 has a centrallypositioned aperture through which a brass guide rod 35 extends. This rodserves to mount the carrier bar 33 in the circuit breaker and a helicalspring 36 is mounted on the rod 35 between a'fixed projection 38extending upwardly from the platform 18, and a surface on the carrierbar 33. The aperture in this carrier bar is elliptical in cross-sectionso that the spring 36 will at all times bear against the edges of suchaperture to urge the lower part of the carrier bar 33 to the right whilepermitting such bar a degree of freedom of tilting motion as later morefully explained. When the spring 36 takes charge urging the carrier bar33 to the right as seen in Figs. 1, 2 and 5 the circuit breaker is inthe open position. The rod 35 is firmly secured to the projection 33 bymeans of a pin 37. The other end of the rod 35 is vertically forked toprovide a vertical recess into which a portion of the mechanism later tobe described may travel, this forking not being visible in the drawings.

The movable contacts 28 cooperate with fixed contacts 39 each formed ofa strip of suitable conducting material, such as copper, and eachsecured to a terminal 41 and to the shell 11 of the circuit breaker bymeans of a rivet 40. These fixed contacts 39 have mounted on their freeends contact-making surfaces 43 inclined to the plane of the platform18.

Fastened directly to the undersurface of the platform 18 by means of ascrew 45 is an ambient temperature compensating device, incorporatingmeans for correcting the operation of the breaker depending upon theambient temperature. This device includes a channelled bracket 46, theflat bottom surface 47 ofwhich is provided with a pair of slots 48 and49 (see Figs. 5 and 7). The two side walls 50 of the bracket 46 have amaximum height at the end nearer the carrier bar 33 and taper to aminimum height at the other end. At the former end a pair of holes aredrilled in the side walls 50 to act as bearings for a shaft 51 whichacts as a pivot for a generally U- shaped bimetallic 'strip 52. One endof the bimetallic strip 52 has an upwardly bent leg 53 projecting intothe transverse passage 19 extending across the platform 18, while theother end thereof is provided with a hole for cooperation with a screw55 which is threaded into the centre of the bar 20 and acts to transmitthe vertical movement of such bar to the bimetallic strip 52.

The manually operated mechanism of the circuit breaker consists of anoperating handle 10 moulded from a suitable non-conducting material inthe shape of a fiat segment of a circle. This operating handle 10 ispivotally mounted on a pin 56 extending between the main side walls 58of a frame member 57 (see especially Figs. 1, 2 and 4), these side walls58 being extended into a pair of wings 59 spaced more widely apart fromeach other than the side walls 58 (Fig. l). The frame member 57 alsoincludes a bottom surface 60 (Figs. 5 and 7) interconnecting the sidewalls 58, and an end surface 61 bent up from such bottom surface 60. Thebottom surface 60 includes a tapped hole into which the fixing screw 45extends, such screw acting to fasten both the bracket 46 and the framemember 57 to the platform 18 of the shell 11. The end surface 61 of theframe member 57 also includes a tapped hole into which an adjustingscrew 62 engages. This screw 62 acts to hold the operating mechanism inthe shell 11, and to position the same relatively to the fixed parts byvirtue of abutment of its head against a moulded projection 63 of theplatform 18. The wings 59 of the frame member 57 are interconnected by apin 64.

The operating mechanism also includes a second frame member 67, slidablymounted in relation to the first frame member 57. This second framemember 67 comprises a pair of side walls 73 joined by an end wall 92 atthe end of the frame member 67 remote from the operating handle 10, anda ledge 68 situated at the end near the operating handle 10. The endwall 92 is perforated to permit passage of the rod therethrough. Theside walls 73 of the second frame member 67 are provided with a pair ofslots which cooperate with the pin 64 extending between the wings 59 ofthe first frame member 57. The spacing apart of the side walls 73 of thesecond frame member 67 is less than the spacing of the wings 59 of thefirst frame member 57, and the sec ond frame member slides between suchwings 59.

The operating mechanism also includes a latch mechanism mounted withinthe frame member 67. The primary element of this latch mechanism is alatch member "/tl pivotally mounted between the side walls 73 of theframe member 67 by means of a pin 71, and having a free end 69 extendingdownwardly and towards the operating handle 10 so as, in the closedposition of the circuit breaker (as seen in Fig. 4) to be in registerwith the upwardly extending bent leg 53 of the bimetallic strip 52.Mounted on a further pin 75 extending between the side walls 73 of theframe member 67, is a cam 77 having a step 76 normally in register withthe end of the latch member remote from the end 69 thereof alreadyreferred to. The cam 77 also has a step 86 arranged to cooperate with afurther pin 79 extending between the side walls 73 of the frame member67. The cam 77 is connected to the operating handle 10 by means of apair of links 89 pivotally mounted both to the cam 77 and to theoperating handle 10 by pins 91 and 90 respectively. The cam 77 is urgedin a clockwise direction, as seen in the side views, by a spring 78mounted on the pin 75. The latch member 70 is urged in a clockwisedirection as seen in the side views, by means of a tongue shaped wirespring 72. A bushing 83 is positioned on the pin between the cam 77 andone of the side walls 73 of the frame member 67, to retain such camcentrally of such frame member, the spring 78 serving a similar purposeon the other side of the cam.

The operating handle 10 isbiased to the open position of the switch, i.e. the position shown in Figs. 2 and 5, by means of a coiled spring 84extending between a projection 85 on the undersurface of the operatinghandle til and a recess 86 formed aroundv a central column 87 projectingfrom the platform 18, an adjusting screw 83 extending through theplatform 18- and along the column 87. The position of this screwdetermines/the limit of anti-clockwise movement of the operating handle10.

The operating mechanism is restrained from lateral displacement by meansof a pair of parallel projections 93 extending upwardly from theplatform 18, and engaging the outer edges of the wings 59 of. the framemember 57.

The carrier bar 33 is formed with a pair of hoods 97 arranged over thecontacts 28, and with a vertically extending central recess in its rearsurface. The face of this recess, which is pressed by the spring 36against the end wall 92 of the second frame member 67, consists of twoinclined portions. The upper portion 99 of this face extends downwardlyand slightly to the rightas seen in Figs. 5 and 6, and the lower portion96 is inclined downwardly and inwardly of the carrier bar 33, these twoportions 99 and 96 forming at their line of junction a ridge 100 whichis the part against which the wall 92 normally bears in the openposition of the switch (see Fig- 5).

The shell 11 of the circuit breaker is moulded to provide two pairs ofarc chutes 101 (Fig. 3) interconnecting cavities 1S and 16 and cavities14- and 17. In longitudinal alignment with these are chutes 101, thereis a further pair of arc chutes 102 (see Fig. 1) formed in the sidewalls of the circuit breaker. A tapped hole 95 is provided in theplatform 18 to receive a screw (not shown) employed for holding thecover 12 in position over the mechanism of the circuit breaker. Thiscover 12 has a slot 103 of conventional design, through which the fingergrip portion of the operating handle 10 extends and along which suchfinger grip portion may travel. A slot 104 is formed in the platform 18to allow movement of the screw 45 on adjustment of the first framenumber 57.

The operation of the circuit breaker is as follows:

in the off position of the circuit breaker, shown in Figs. 2, 5 and 9the carrier bar 33 carrying the moving contacts 28 is in its extremeright hand position and is pressed lightly by the spring 36 against theend wall 92 of the second frame member 67. In this position the bar 33is tilted somewhat anti-clockwise, as seen in Figs. 2, 5 and 9. When thecircuit breaker is to be placed in the on position, the operating handleit) is moved manually in an anti-clockwise direction to exert a closingforce, as demonstrated by the arrow C in Figs. 9 to 11, acting throughthe wall 92. The carrier bar may be considered as having two motions:

(a) Translatory motion between a contacts-disengaged position and acontacts-engaged position (this takes place along the line X whichdefines the axis of the rod 35); and

(b) Limited tilting motion, about ridge 100, between two orientations.

The first orientation is such that the plane P2 defined by the fiatcontact-making surfaces of the bar-mounted contacts 34 is parallel tothe plane P1 defined by the contact-making surfaces of the fixedcontacts 43. This orientation is illustrated in Figure 11, where theplanes P1 and P2 are in fact coincident, the contacts 34 and 43 beingfully engaged face to face. This view corresponds to Figure 4 of thestructural drawings and the on position of the circuit breaker.

The second tilted orientation is defined as being such that thebar-mounted contacts 34 are displaced towards the fixed contacts 43 withthe planes P1 and P2 inclined to each other. This second orientation ofthe bar is illustrated in Figure 10, while as already indicated Figure 9shows the relaxed condition when the switch is fully open and before theclosing force C or opening force 0 have any significant tilting effect.

The spring means (force 0) urge the bar 33 both into contacts-disengagedposition, i. e. to the right in respect of translatory motion, and intothe second tilted orientation, i. e. anti-clockwise" about the point ofcontact of the ridge and the plate 92. The closing means (force C) acton the bar 33 for moving such bar against the force 0 from thecontacts-disengaged position towards the contacts-engaged position. Theinitial effect of the operation of such closing force is demonstrated inFigure 10 in which the main part of the translatory motion of the bartowards the engaged position has taken place, and in which the springmeans, which began effectively to tilt the bar to its second orientationas soon as the closing translatory movement began, still prevail to holdthe bar in such second tilted orientation. It will thus be apparent thatthe closing means are such as to move the bar towards contacts-engagedposition to effect tilting of said bar from said second orientation tosaid first orientation on engagement of the contacts,.the manner of thisoperation appearing from a comparison of Figures 10 and 11. Once thecontacts touch there will be a reaction force exerted by the fixedcontacts 43 on the bar-mounted contacts 34. This force is indicated bythe arrow R in Figure 10 and it will be seen that it acts substantiallyalong the surface S (which is the imaginary surface traced out by thecentre points of the bar-mounted contacts in moving in contacts-engagedposition) and thus exerts a clockwise turning moment on the bar aboutits point of pivot which is the ridge 16f}. This clockwise turningmoment will overcome the anti-clockwise turning moment of the combinedforces 0 and C so that the bar will be turned from the second to thefirst tilted orientation with the contact surfaces engaging firmly withtheir faces in the same coincident plane, i. e. the Figure 11 condition.If the circuit breaker were of the single pole type which is within thecontemplation of the invention, then the surface S traced out by theline joining the centre points of the bar mounted contacts iseffectively replaced by a line traced out by movement of the singlebar-mounted contact.

In the closed position of the circuit breaker the pin 90 is below theline joining the pin 91 to the pivot pin 56 of the operating handle 10,so that the compression force in the links 89 acts to hold the operatinghandle in the newly acquired position against the force of the spring84.

The operation just described whereby the contact surfaces 34 and 43 actto rotate the carrier bar 33 causes them to slide along one another toproduce a wiping and rolling action between the individual contacts ofeach pair which is highly advantageous for cleaning the surfaces. Thisaction takes place both in closing and opening of the circuit breaker.The reverse action on opening of the circuit breaker facilitatesseparation of the surfaces 34 and 43 in the event that there may havebeen some welding action between such surfaces due to over-heating.

It is a further valuable feature of the invention that one single mainspring 36 is used both to open the circuit breaker on tripping and alsoto provide pressure between the contacts when the circuit breaker isheld in the closed position by the toggle-like mechanism of links 89 andoperating handle 10. This main spring provides the contact pressure byvirtue of the low position at which it bears against the carrier bar 33.The force 0 of the spring when it is compressed in the closed positionof the circuit breaker (Figure 11) tends to rotate the carrier bar 33anticlockwise about the ridge 109. This anticlockwise turning momentforces the contact surfaces 34 and 43 firmly together.

During the movement of the circuit breaker from the off to the onposition the cam 77 has acted merely to transmit the force applied tothe operating handle 10, and has remained in its extreme clockwiseposition, being held in this position by the latch member 70. The cam 77then lies between the forked ends of the rod 35.

If the circuit breaker is to be moved manually from the on position tothe off position, this is accomplished by movement of the operatinghandle 10 in the clockwise direction with simple reversal of themovements already described.

On' i h e occurrence of an overload on either of the two circuitscontrolled by this circuit breaker, one or other or both of thebimetallic strips 23 will be caused to flex and press upwardly on thescrews 24 of the bosses 21 of the totalizing bar 20. This has the effectof elevating the centre of such bar to an extent dependent upon the mainelevation of the two ends of the bar 20. The movement of the center ofthe bar 20 is thus a function of the total overload in the two circuitsflowing through the circuit breaker.

As fully explained in United States Patent No. 2,600,734, issued to W.A. Coburn, June 17, 1952, the arrangement of a totalizing bar with apair of bimetallic strips engaging each end of the bar provides amovement of the centre of the bar which is particularly suitable foroperation of the tripping mechanism of a circuit breaker employed in athree-wire single phase type of supply circuit. It is common, forexample, to rate such a totalizing circuit breaker as, say, 25-41 amps.This means that with a perfectly balanced load the circuit breaker willtrip at a given overload, usually approximately 125 percent, of a ratedload of 25 amps. in each strip, i. e. in each half of the three-wirecircuit. When the load is totally unbalanced, that is to say if all theload is on one half of the three-wire circuit, all the current will passthrough one of the bimetallic strips and no current will pass throughthe other. Under these conditions the breaker will trip at the sameoverload (125 percent) on the rated current of 41 amps. in the loadedstrip. It will be noted that this current of 41 amps. in one half of thecircuit represents 82 percent of the load that would be imposed upon thesecondary of the transformer from which the circuit is supplied withbalanced currents of 25 amps. in each half of the circuit. Approximatelypercent of the transformer rated load is normally about the maximum loadthat can be safely imposed upon one half of the secondary of a normalsupply transformer when the other half of the transformer is unloaded.

The fact that it does not require 50 amps. in one of the strips, whenthe other strip carries no current, to move the centre point of thetotalizing bar the same distance as it would be moved by a current of 25amps. in each of the strips, follows from the fact that the heatgenerated in each strip is a function of the square of the currentpassing through such strip. This tends to reduce the unbalanced currentat which the circuit breaker will trip, but acting to increase thicurrent is the further fact that the rate of loss of heat from thebimetallic strip carrying the high load is disproportionately great byreason of its higher temperature. The former factor prevails however andin most cases reduces the unbaianced tripping current to about 80percent of the sum of the two balanced currents. Special provision canbe made for varying this percentage by control of the heat dissipationfrom the bimetallic strips or by variation of the manner in which thestrips are connected to the totalizing bar. The strips may be connectedother than through the adjusting screws 24, and, in particular, they maybear directly against flat surfaces on the ends of the totalizing bar sothat, as such bar is tilted, edges of the strips rather than flatsurfaces thereof engage the bar, these edges then being at differentdistances from the central point of the bar. In this Way the lever armsbetween the strips and the centre of the bar can be varied, leading tovariation in the percentage of the full load at which the circuitbreaker can be tripped by a fully unbalanced load.

It will be appreciated that, in practice, a completely balanced or acompletely unbalanced load is seldom obtained. With semi-unbalancedloads conditions intermediate between the two extremes alreadydiscussed, will pertain.

In the circuit breaker under consideration as an embodiment of thepresent invention, the upward movement of the centre of the totalizingbar 20 is transmitted through the screw 55 to the bent bimetallic strip52 and thus to the upwardly bent leg 53 thereof by rotation of the strip52 as a whole about the pin 51. When an overload for which the circuitbreaker has been set, is reached, the leg 53 will have been movedupwardly sufficiently to come into contact with the end 69 of the latchmember 70, to force such end 69 upwardly and rotate the latch member 70about its pivot pin 71 until the other end of such latch member 70 ismoved away from the step 76 on the cam 77. This movement frees the cam77 for anti-clockwise rotation. Only a slight anti-clockwise rotation ofthis cam is necessary to reduce the com pression in the links 89sufficiently to allow the spring 84 acting on the undersurface of theoperting handle 10 to take charge of such operating handle 10 and rotateit clockwise. Fig. 7 has been provided to illustrate the positions thatthe parts will assume instantaneously very shortly after this trippingaction. As soon as the toggle type of mechanism formed by the links 89has thus been broken, the spring 36 takes charge of the carrier bar 33to return it to the off position. Moreover, as the parts begin to movebackwardly to the off position, the spring 78 returns the cam 77 to itsoriginal position with the step 89 abutting against the pin '79 andpreventing further clockwise rotation. This return movement of the cam77 moves the step '76 to the left again so that the end of the latchmember '70 may move up into re-engagement therewith as soon as the leg53 of the bimetallic strip 52 has moved downwardly after sufficientcooling of the bimetallic strips 23.

The purpose of the bimetallic strip 52 is to compensate for variationsof ambient temperature. The effect of this compensation is illustratedby the diagram of Figure 8 which shows approximately the balanced loadperformance of a totalizing circuit breaker rated at 254l amps, firstlywithout ambient temperature compensation (line A) and secondly withambient temperature compensation (line B). The diagram of Figure 8 hasbeen prepared on the basis of a completely balanced lead butcorresponding effects would be obtained with partly and whollyunbalanced loads. It will be seen from the temperature scale forming theabscissa of this diagram that the uncompensated circuit breaker has beenadjusted to provide correct operation at a temperature of 72 F., i. e.the temperature at which line A crosses the scale marking of 3t amps, i.e. approximately 125 percent of the rated 25 amps. To the right of thispoint on the diagram, that is to say under the conditions likely tooccur in summer, especially if the circuit breaker is exposed to thedirect rays of the sun, it will be seen that line A drops well belowline B and that at the extreme edge of the diagram, i. e. 140 F., thecircuit breaker will trip at a balanced load of approximately 22 amps,which is even below the rated tripping current and allows no provisionfor overload. The reason for this drop of the curve, is, of course, thatthe main operating bimetallic strips 23 are already considerably heatedby the atmosphere before the effects of the current are felt. Since itis common to settle the terms of supply of electric power to theconsumer on a basis of the maximum demand that the consumer may drawfrom the mains, as determined by the setting of the circuit breaker, theconsumer will clearly be penalized under these conditions.

On the other hand, in winter, when the heat supplied by the current tothe bimetallic strips will be required to compensate for the effects ofthe low ambient temperature, the consumer will be able to draw from themains a current in excess of that agreed upon with the utility as beinghis maximum. Under these conditions it is the supplying utility thatsuffers, as is illustrated by the left-hand end of line A.

It will be seen from line B that when an auxiliary bimetallic strip isemployed substantially a uniform tripping of the circuit breaker at 125percent overload of the rated current will be achieved at all normaloperating temperatures. To achieve this effect, it is theoreticallydesirable to make the bimetallic strip 52 equal in effective length toeach of the bimetallic strips 24. As a practical matter, the length ofthe bimetallic strip 52 will normally be made slightly greater than thelength of each of the strips 24 in order to off-set a slight loss oflever arm incurred in transmitting the movement of the tripping forcethrough the strip 52 to the latch mechanism.

An important feature of the present invention is the arrangement of theambient temperature compensating strip 52 in a cavity of the shell ofthe circuit breaker well insulated from the cavities in which the mainbimetallic strips 24 are housed. If this were not so, the strip 52 wouldtend to have its temperature raised above the ambient temperature bytransfer of heat from the main strips 24. The particular arrangement ofthe embodiment of the invention illustrated in the accompanying drawingsin which a centrally raised platform 18 forms at each side the cavitiesl6 and 317 for the strips 24, while underneath providing the cavity 15for the compensating strip 52, is a particularly satisfactory andcompact arrangement which admirably accomplishes this end.

Other important features of the invention are the wiping and rollingaction which takes place when the contact surfaces 34 and 43 are broughttogether (by virtue of the ridge on the carrier bar 33) and the reversewiping and rolling action which takes place when the circuit breaker isopened. This reverse action, i. e. a sliding one upon the other of thecontact surfaces 34 and 43 greatly facilitates separation of thesesurfaces in the event that there may have been some welding actionbetween such surfaces due to over-heating.

It is also a valuable feature of the invention that one single mainspring 36 is used both to open the circuit breaker on trippingand alsoto provide pressure between the contacts when the circuit breaker isheld in the closed position shown in Figure 4 by the toggle-likemechanism of links 89 and operating handle 10. This main spring providesthe contact pressure by virtue of the low position at which it bearsagainst the carrier bar 33. The force of the spring when it iscompressed in the closed position of the circuit breaker tends to rotatethe carrier bar 33 anti-clockwise about the ridge lltiti which issituated above the point of bearing of the spring 36 against such bar,as seen from Figures 2, 4, 5 and 7. This anti-clockwise turning momentforces the contact surfaces 34 and 43, which in turn are above the levelof the ridge 100, firmly together.

Under certain circumstances, such as when the manufacturing costs are ofparamount importance, the ambient temperature compensating device andits supporting parts may be omitted from the circuit breaker, thetotalizing bar then bearing directly on the latch member 78 or throughsome suitable direct connection.

I claim:

1. An electric circuit breaker having a pair of fixed contacts, a pairof ganged contacts movable into and out of contact each with one of saidfixed contacts whereby to make and break a pair of independent electriccircuits, a totalizing bar, a pair of main bimetallic elements eacharranged to be heated by the current in one of said circuits and eachacting on one end of said totalizing bar, a latch mechanism for trippingthe movable contacts, arranged for actuation by movement of a part ofsaid bar intermediate its ends, and auxiliary bimetallic means arrangedin the path of transmission of movement from said main bimetallicelements to said latch mechanism, said auxiliary bimetallic means beingarranged so as to compensate for deflection of the main bimetallicelements due to ambient temperature fluctuations.

2. An electric circuit breaker having a pair of fixed contacts, a pairof ganged contacts movableinto and out of contact, each with one of saidfixed contacts whereby to make and break a pair of independent electriccircuits, a totalizing bar, a pair of main bimetallic elements eacharranged to be heated by the current in one of said circuits and eachacting on one end of said totalizing bar, a latch mechanism for trippingthe movable contacts, and an auxiliary bimetallic element co-acting witha part of said bar intermediate its ends to transmit movement thereof tosaid latch mechanism, said auxiliary bimetallic element being arrangedso as to compensate for deflection of the main bimetallic elements dueto ambient temperature fluctuations.

3. A circuit breaker as claimed in claim 2, wherein said auxiliarybimetallic element is separated from said main bimetallic elements bypartition walls.

4. A circuit breaker as claimed in claim 2, including a rectangularsupporting shell of insulating material having a central longitudinallyextending platform with partition walls depending from the lateral edgesthereof to define a pair of longitudinally extending lateral cavities onone face of the shell and a longitudinally extending central cavity onthe other face of the shell, the latter cavity being separated from theformer cavities by said partition walls, wherein said main bimetallicelements are in the form of elongated strips each extending along one ofsaid lateral cavities, and the auxiliary bimetallic element is in theform of an elongated strip disposed in the central cavity. a

5. A circuit breaker as claimed in claim 4, wherein the auxiliarybimetallic strip is bent upon itself, one end of said strip beingcoupled with the intermediate point of the totalizing bar while theother end is positioned for cooperation with said latch mechanism, whichlatter is mounted on said platform.

6. An electric circuit breaker having a pair of fixed contacts mountedin side-by-side relationship, a rod, an elongated bar extendingtransversely to said rod and loosely slidably mounted at its centrethereon, said bar carrying a contact at each end positioned forcooperation with one of said fixed contacts, closing means for movingsaid bar to contacts-engaged position, a coil spring extending alongsaid rod between a fixed abutment and a surface of said bar and urgingsaid bar to contacts-disengaged position, a surface on the centre ofsaid bar presenting to said closing means a longitudinally extendingridge parallel to the line joining the contacts mounted on said bar,said ridge lying in a plane intermediate between and parallel to a pairof mutually parallel planes in one of which lies said line and in theother of which lies the longitudinal axis of the rod.

7. An electric circuit breaker having a pair of fixed contacts countedin side-by-side relationship, a loosely slidably mounted bar carrying apair of contacts positioned each for engagement with a respective one ofsaid fixed contacts, spring means urging said bar to contacts-disengagedposition, said spring means acting on said bar at a point displaced froma surface generated by the line joining the center points of thebar-mounted contacts in moving into contacts-engaged position, andclosing means for moving said bar to contacts-engaged position, saidclosing means acting on said bar between said surface and the planeparallel thereto which passes through the point of said bar acted uponby the spring means.

8. An electric circuit breaker having a pair of fixed contacts mountedin side-by-side relationship, a loosely slidably mounted elongated barcarrying a contact on each end positioned for engagement with arespective one of said fixed contacts, spring means urging said bar tocontacts-disengaged position, said spring means acting on a centralpoint of said bar intermediate between said bar-mounted contacts anddisplaced from a surface generated by the line joining the center pointsof the barmounted contacts in moving into contacts-engaged position, andclosing means for moving said bar to contacts-engaged position, saidclosing means acting centrally on said bar between said surface and thepart of said bar acted upon by said spring means.

9. An electric circuit breaker having a pair of fixed contacts mountedin side-by-side relationship, a loosely horizontally slidably mounted,elongated, horizontally extending bar carrying a contact at each endpositioned for engagement with a respective one of said fixed contacts,spring means urging said bar to contacts-disengaged position, saidspring means acting on a central part of said bar intermediate betweensaid bar-mounted contacts and at a level different from that of asurface generated by the line joining the center points of thebar-mounted contacts in moving into contacts-engaged position, andclosing means for moving said bar into contacts-engaged position, saidclosing means acting centrally on said bar at a level between saidsurface and the level at which said spring means act on said bar.

10. An electric circuit breaker having a fixed contact, a looselyslidably mounted member carrying a contact positioned for co-operationwith said fixed contact, opening means acting continuously on saidmember to urge it to contacts-disengaged position, said opening meansacting on a part of said member displaced from a line generated by thecenter point of the member-mounted contact in moving intocontacts-engaged position, and closing means having flat contact-makingsurfaces lying in a first common plane; a bar carrying a pair ofcontacts for cooperation each With a respective one of said fixedcontacts, such bar-mounted contacts having flat contactmaking surfaceslying in a second common plane; means mounting said bar for translatorymotion between a contacts-disengaged position and a contacts-engagedposition and for limited tilting motion between two orientations, saidtilting motion being about an axis parallel to the line joining thebar-mounted contacts, the first of said orientations being such thatsaid planes are parallel to each other and the second of saidorientations being such that the bar-mounted contacts are displacedtowards the fixed contacts with said planes inclined to each other;spring means urging said bar to contacts-disengaged position and intosaid second tilted orientation; and closing means for effectingtranslatory movement of said bar against the force of said spring meansfrom contactsdisengaged into contacts-engaged position whereby to eifecttilting of said bar from said second orientation to said firstorientation on engagement of said contacts.

12. An electric circuit breaker comprising: a pair of fixed contactsmounted in side-by-side relationship and having flat contact-makingsurfaces lying in a first common plane; a bar carrying a pair ofcontacts for cooperation each with a respective one of said fixedcontacts, such bar-mounted contacts having fiat contact-making surfaceslying in a second common plane; means mounting said bar for translatorymotion between a contacts-disengaged position and a contacts-engagedposition and for limited tilting motion between two orientations, saidtilting motion being about an axis parallel to the line joining thebar-mounted contacts, the first of said orientations being such thatsaid planes are parallel to each other and the second of saidorientations being such that the bar-mounted contacts are displacedtowards the fixed contacts with said planes inclined to each other;spring means urging said bar to contacts-disengaged position and intosaid second tilted orientation; and closing means for effectingtranslatory movement of said bar against the force of said spring meansfrom contactsdisengaged into contacts-engaged position whereby to etfecttilting of said bar from said second orientation to said firstorientation on engagement of said contacts, said spring means acting ona part of said bar displaced from a surface generated by the linejoining the center points of the bar-mounted contacts in moving intocontacts engaged position, and said closing means acting on said barbetween said surface and the plane parallel thereto which passes throughthe point of said bar acted upon by said spring means.

13. An electric circuit breaker comprising a fixed contact having a flatcontact-making surface defining a first plane, a loosely slidablymounted member carrying a contact positioned for co-operation with saidfixed contact, such member-mounted contact having a flat contactmakingsurface defining a second plane, means mounting said member fortranslatory motion between contactsdisengaged position andcontacts-engaged position and for limited tilting motion between twoorientations, such tilting motion being about an axis generallytransverse to a line generated by the center point of the membermountedcontact in moving into contacts-engaged position, the first of saidorientations being such that said planes are parallel to each other andthe second of said orientations being such that the member-mountedcontact is displaced towards the fixed contact with said planes inclinedto each other, spring means acting on said member to urge it tocontacts-disengaged position and into said second tilted orientation,and closing means for etfecting translatory movement of said memberagainst the force of said spring means from contacts-disengaged intocontacts-engaged position whereby to effect tilting of said member fromsaid second orientation to said first orientation on engagement of saidcontacts, the manner of mounting of said member being such that inmoving into contacts-engaged position, said membermounted contact wipesacross the face of said fixed contact.

References Cited in the file of this patent UNITED STATES PATENTS1,886,477 Getchell Nov. 8, 1932 12 OKeeffe May 23, 1933 Jackson Oct. 11,1938 Von Hoorn Dec. 26, 1939 Van Valkenburg et al. Aug..19, 1947Overturf Feb. 8, 1949 Randell Ian. 8, 1952 Coburn June 17, 1952Ingwersen Jan. 13, 1953 Allen Oct. 20, 1953 Dyer et a1. Jan. 19, 1954Cole et a1 June 15, 1954 Cellerini et a1 Nov. 2, 1954 Hulbert Mar. 1,1955 Walton et a1. June 5, 1956 FOREIGN PATENTS France Nov. 3, 1938

